The present invention relates to a sample bag for collecting a mixture of gasses for analysis, and to a method of collecting a diluted exhaust gas mixture from an internal combustion engine.
A gas diluting and testing apparatus is used to analyze, among other things, vehicular exhaust. The apparatus uses a mixing system to dilute the exhaust gasses so that the moisture content of the gasses is sufficiently reduced in order to minimize errors due to condensation. One example of an existing mixing system is the constant volume sampler (CVS).
The CVS has been used for over twenty-five years to sample the emissions from automobiles. It is the device used for automotive emissions tests that are the basis for the certification that vehicles sold in the United States are compliant with the Clean Air Act.
Automotive sampling systems, as well as other analytical systems, utilize sealed bags for collecting engine exhaust gasses for analysis of components after the collection interval has been completed. In order to preserve the integrity of the captured sample, the sample bag material must be inert, non-reactive, without leaks, and must have low permeation for the specific gasses contained both within the bag and outside the bag. The sample bag must not emit or absorb gasses, and the bag material must be flexible for fill and empty cycling. In the past, materials used for construction of the sample bag walls have failed to meet one or more of the above criteria, and it is desirable to provide a sample bag that limits these various undesirable characteristics. As vehicles become cleaner, their emissions become more difficult to measure accurately. To overcome some of the inherent limitations of the CVS, some attempts have been made to develop improved mixing systems. In addition to the effects of the mixing system itself, mixing systems that collect a gas mixture with a sample bag may sometimes be limited in accuracy due to limitations of the sample bag.
Although many existing mixing systems and existing sample bags have been used in applications that are commercially successful, with increasing demands for more accurate measurement techniques, it is desirable to make improvements to existing measurement and dilution techniques for analysis of gaseous constituents.
It is, therefore, an object of the present invention to provide a sample bag for collecting a mixture of gasses for analysis that is made of a modified polymer that limits the effects of diffusion through the bag walls and limits the effect of residual gasses within the bag walls on the integrity of the collected sample.
In carrying out the above object and other objects and features of the present invention, a sample bag for collecting a mixture of gasses for analysis is provided. The sample bag is made of a modified polymer consisting essentially of tetrafluoroethylene (TFE) and at most about 2.0 percent perfluoropropylvinylether (PPVE). The modified polymer is melt processable, unlike conventional polytetrafluoroethylene (PTFE). Because the modified polymer may be heat sealed and bonded to itself by various welding techniques, the modified polymer reduces the effects of diffusion through the sample bag walls and residual gasses in the sample bag walls.
The amount of perfluoropropylvinylether (PPVE) co-monomer in the modified polymer may vary depending on the desired properties for the sample bag. That is, the modified polymer for the sample bag consists essentially of tetrafluoroethylene (TFE) and at most about 2.0 percent perfluoropropylvinylether (PPVE), and preferably, at most about 1.5 percent perfluoropropylvinylether (PPVE). More preferably, the modified polymer includes at most about 1.0 percent perfluoropropylvinylether (PPVE) co-monomer. More preferably, the modified polymer includes at most about 0.3 percent perfluoropropylvinylether (PPVE). More preferably, the modified polymer includes at most about 0.2 percent perfluoropropylvinylether (PPVE) co-monomer. More preferably, the modified polymer includes at least about 0.05 percent perfluoropropylvinylether (PPVE) co-monomer. In a suitable application, the modified polymer includes about 0.1 percent perfluoropropylvinylether (PPVE). It is appreciated that the percentages are mass percentages, as is readily understood by one skilled in the polymer arts.
Further, in carrying out the present invention, a method of collecting a diluted exhaust gas mixture from an internal combustion engine is provided. The method comprises receiving an exhaust gas mixture, receiving a dilution gas, mixing the dilution gas with the exhaust gas mixture to form the diluted exhaust gas mixture, and collecting the diluted gas exhaust gas mixture in a sample bag. The sample bag is made of a modified polymer consisting essentially of tetrafluoroethylene (TFE) and at most about 2.0 percent perfluoropropylvinylether (PPVE). It is appreciated that the amount of perfluoropropylvinylether (PPVE) co-monomer in the modified polymer may vary depending on the particular desired properties for the sample bag.
Still further, in carrying out the present invention, a sample bag for collecting diluted exhaust gasses from an internal combustion engine is provided. The sample bag comprises a boundary structure and an inlet connected to the structure for receiving the gasses. The boundary structure defines a container for the gasses. The structure is made of a modified polymer consisting essentially of tetrafluoroethylene (TFE) and at most about 2.0 percent perfluoropropylvinylether (PPVE). It is appreciated that the amount of perfluoropropylvinylether (PPVE) co-monomer may vary depending on the particular application and properties desired for the sample bag.
The advantages associated with embodiments of the present invention are numerous. For example, a sample bag for collecting a mixture of gasses for analysis that is made of the modified polymer consisting essentially of tetrafluoroethylene (TFE) and at most about 2.0 percent perfluoropropylvinylether (PPVE) reduces the effects of diffusion through the bag walls and the effects of residual gasses in the bag walls (emission and absorption by the walls) on the integrity of the sample. That is, a sample bag made of the modified polymer overcomes limitations associated with other sample bags including sample bags made of pure polytetrafluoroethylene (PTFE).
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.